Fluid heater with low porosity thermal mass

BACKGROUND

0001This invention relates, in general, to fluid heater apparatus and, more particularly, to fluid heater apparatus which provides a heated wash fluid to a cleanable surface, and, still more specifically, to a heated wash fluid apparatus for a vehicle windshield wash system.

0002It is necessary in many diverse applications to quickly elevate the temperature of a fluid to a higher use temperature. For example, it is desirable to be able to provide instant hot water, for use in homes, offices and campers, as well as for industrial processes.

0003In cleaning applications, it is known that hot fluid removes dirt and other debris from a surface much better and much faster than colder fluids. One heated fluid application is a vehicle wash fluid system, such as a windshield wash system as well as vehicle wash systems applied to camera lenses, exterior lamps and lamp lenses, mirrors, etc. Vehicles are typically provided with at least one and usually multiple windshield washers which are used to clear the field of vision in a windshield or rear backlight.

0004Typically, a nozzle or spray device is provided adjacent to or as part of the windshield wiper to disperse a pattern of wash fluid onto the windshield prior to and during the wiping operation to improve the efficiency of the wiping operation so as to provide a clear field of vision for the driver or vehicle passengers. The wash fluid is typically stored in a reservoir in the engine compartment and is pumped through the spray device upon manual activation of a control actuator by the vehicle driver.

0005Since it is known that warm or heated fluid provides better cleaning efficiency than cold fluid, it is known to provide a heated wash fluid to a vehicle window spray device. Various wash fluid heating devices have been developed, but all typically utilize a heat exchanger design wherein a heat source is disposed in a body through which the wash fluid flows. The wash fluid picks up heat in the heat exchange body which elevates its temperature prior to dispersion through the spray nozzle onto a vehicle window.

0006Thus, it would be desirable to provide a fluid heater apparatus providing a heated fluid which has a thermal mass with high thermal conductivity.

SUMMARY

0007The present invention is a fluid heater apparatus and method of making the same.

0008In one aspect, the heater apparatus includes a low porosity, thermally conductive mass, heating means thermally coupled to the thermally conductive mass for imparting heat to the thermally conductive mass, and a fluid flow path formed in the thermally conductive mass between an inlet and an outlet. Fluid in the fluid flow path absorbs heat from the thermally conductive mass, which heat is imparted to the mass by the heating means.

0009In another aspect, a wash apparatus includes a fluid reservoir contain a wash fluid, a pump coupled to the fluid reservoir for pumping fluid from the reservoir, a spray nozzle fluidically coupled to the pump for discharging fluid pumped from the reservoir onto a cleanable surface, and the heater apparatus disposed in fluid flow communication between the pump, the reservoir and the nozzle.

0010In one aspect, the thermally conductive mass is cast from a material in a semi-solid state. In another aspect, the thermally conductive mass is formed of molded ceramic. In yet another aspect, the thermally conductive mass is formed of an extruded material. The extruded thermally conductive mass can be formed of one of a ceramic material, aluminum and poltruded carbon.

0011The thermally conductive mass includes a plurality of throughbores extending through first and second ends. Means are provided for mounting the heater means in the thermally conductive mass concentrically within and surrounded by the plurality of throughbores. Means are also provided for coupling a fluid inlet to one end of each of a plurality of throughbores and a fluid outlet to each of the other ends of the plurality of throughbores to define the fluid flow path as at least one parallel flow path between the inlet and the outlet through the plurality of throughbores.

0012In another aspect, the present invention is a method for making a fluid heater. The method includes the steps of:

0013providing a thermally conductive mass formed of a low porosity material, the mass having at least one fluid flow channel extending therethrough, the fluid flow channel having first and second ends;

0014mounting heater means in the thermally conductive mass, the heater means supplying heat, when activated, to the thermally conductive mass; and

0015fluidically coupling a fluid inlet to one end of the fluid flow channel and a fluid outlet to the other end of the fluid flow channel to define a fluid flow path between the inlet and the outlet wherein fluid in the fluid flow path absorbs heat from the thermally conductive mass.

0016The method of providing the thermally conductive mass further includes the step of forming the thermally conductive mass of one of aluminum, ceramic and poltruded carbon.

0017The method of providing the thermally conductive mass further includes the step of forming the thermally conductive mass by one of molding and casting.

0018The method of providing the thermally conductive mass further includes the step of forming the thermally conductive mass of a material cast at a semi-solid material temperature.

0019The method of providing the thermally conductive mass further includes the step of extruding the thermally conductive mass from a low porosity material.

0020The method of providing the thermally conductive mass further includes the step of extruding the thermally conductive mass as a one piece, monolithic body.

0021The method of providing the thermally conductive mass further includes the steps of forming the fluid flow channel as at least one throughbore extending between first and second ends in the body, and forming the at least one throughbore in a helical path between the first and second ends.

0022The method of providing the thermally conductive mass further includes the steps of forming the thermally conductive mass of a plurality of lamina, each lamina carrying an aperture defining a portion of the throughbore, and another aperture defining a portion of a bore for receiving a heater means.

0023The present invention provides a highly thermally conductive mass for use in a fluid heater apparatus for elevating the temperature of a fluid, particularly a wash fluid, by a unique combination of material and forming process. The mass can be formed of various materials which expand the material options for forming the thermally conductive mass to suit a particular application and/or fluid application temperature. The thermally conductive mass can also be formed of different manufacturing processes which contribute to a lower manufacturing cost, and lower porosity for higher thermal conductivity by minimizing air voids within the mass.

0024The use of the semi-solid material temperature to cast the thermally conductive mass provides a lower die temperature than the prior use of completely liquid, molten casting material. This lower die temperature protects the sealing member used to seal the fluid flow channel within one aspect of the thermally conductive mass.

BRIEF DESCRIPTION OF THE DRAWING

0025The various features, advantages and other uses of the present invention will become more apparent by referring to the following detail description and drawing in which:

0026<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a fluid heater apparatus according to the present invention used in an exemplary vehicle window wash fluid delivery system;

0027<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view of a heater module or the fluid heater apparatus according to one aspect of the present invention;

0028<figref idref="DRAWINGS">FIG. 3</figref> is an exploded perspective view of the heater module shown in <figref idref="DRAWINGS">FIG. 2</figref>;

0029<figref idref="DRAWINGS">FIG. 4</figref> is a partially broken away, perspective view of the assembled heater module shown in <figref idref="DRAWINGS">FIG. 2</figref>, oriented with the circuit board upward;

0030<figref idref="DRAWINGS">FIG. 5</figref> is a partially broken away, perspective view of the heater module shown in <figref idref="DRAWINGS">FIG. 2</figref>, with the opposite surface oriented upward;

0031<figref idref="DRAWINGS">FIG. 6</figref> is a perspective view of the heater module in the orientation of <figref idref="DRAWINGS">FIG. 5</figref> of the present invention, without the covers and the circuit board;

0032<figref idref="DRAWINGS">FIG. 7</figref> is a perspective view of the circuit board side of the heater module, without the covers;

0033<figref idref="DRAWINGS">FIG. 8</figref> is a perspective view of the opposite orientation of the heater module shown in <figref idref="DRAWINGS">FIG. 7</figref>;

0034<figref idref="DRAWINGS">FIG. 9</figref> is a top perspective view of the heater module thermal mass;

0035<figref idref="DRAWINGS">FIG. 10</figref> is a bottom elevational view of the heater module thermal mass shown in <figref idref="DRAWINGS">FIGS. 6–8</figref>;

0036<figref idref="DRAWINGS">FIG. 11</figref> is an enlarged plan view of the heater module shown in <figref idref="DRAWINGS">FIGS. 6–8</figref>;

0037<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view generally taken along line <b>12</b>—<b>12</b> in <figref idref="DRAWINGS">FIG. 11</figref>;

0038<figref idref="DRAWINGS">FIG. 13</figref> is a cross-sectional view generally taken along line <b>13</b>—<b>13</b> in <figref idref="DRAWINGS">FIG. 11</figref>;

0039<figref idref="DRAWINGS">FIG. 14</figref> is a plan view of the freeze protection element shown mounted over the seal on one surface of the thermal conductive;

0040<figref idref="DRAWINGS">FIG. 15</figref> is a side elevational view of another aspect of a heater module which an alternate fluid expansion member according to the present invention; and

0041<figref idref="DRAWINGS">FIG. 16</figref> is a cross-sectional view, generally similar to <figref idref="DRAWINGS">FIG. 12</figref>, but showing another aspect of the present invention.

0042<figref idref="DRAWINGS">FIG. 17</figref> is a top perspective view of another aspect of the heater apparatus of the present invention;

0043<figref idref="DRAWINGS">FIG. 18</figref> is an exploded, perspective view of the heater apparatus shown in <figref idref="DRAWINGS">FIG. 17</figref>

0044<figref idref="DRAWINGS">FIG. 19</figref> is a bottom perspective view of the heater apparatus shown in <figref idref="DRAWINGS">FIGS. 17 and 18</figref>;

0045<figref idref="DRAWINGS">FIG. 20</figref> is an inside perspective view of the top end cover of the heater apparatus shown in <figref idref="DRAWINGS">FIG. 18</figref>;

0046<figref idref="DRAWINGS">FIG. 21</figref> is a perspective view of the base and cover of the heater apparatus shown in <figref idref="DRAWINGS">FIG. 18</figref>;

0047<figref idref="DRAWINGS">FIG. 22</figref> is a top perspective view of the connector housing of the heater apparatus shown in <figref idref="DRAWINGS">FIG. 18</figref>;

0048<figref idref="DRAWINGS">FIG. 23</figref> is a bottom elevational view of the connector housing shown in <figref idref="DRAWINGS">FIG. 22</figref>;

0049<figref idref="DRAWINGS">FIG. 24</figref> is a perspective view of a terminal lead assembly shown in <figref idref="DRAWINGS">FIGS. 18</figref>, <b>22</b> and <b>23</b>;

0050<figref idref="DRAWINGS">FIG. 25</figref> is a plan elevational view of a heat exchange lamina used in the heater apparatus of the present invention;

0051<figref idref="DRAWINGS">FIG. 26</figref> is a partly broken away, partial perspective view of the assembled heat exchange stack of the heater apparatus according to the present invention;

0052<figref idref="DRAWINGS">FIG. 27</figref> is a side elevational view of the complete heat exchange stack of the heater apparatus shown in <figref idref="DRAWINGS">FIG. 18</figref>;

0053<figref idref="DRAWINGS">FIG. 28</figref> is a side elevational, pictorial representation of the helical flow paths through the heat exchange stack shown in <figref idref="DRAWINGS">FIG. 27</figref>, with the outer housing broken away and the circularly disposed, helical flow paths shown pictorially in a two dimensional representation; and

0054<figref idref="DRAWINGS">FIG. 29</figref> is a partial, enlarged view of one of the heat exchange stack lamina according to the present invention.

DETAILED DESCRIPTION

0055Referring now to <figref idref="DRAWINGS">FIG. 1</figref>, there is depicted an environment in which a heater apparatus or module <b>10</b> constructed in accordance with the teachings of the present invention can be advantageously utilized. Although the following use of the heater module <b>10</b> of the present invention is described in conjunction with a vehicle window wash system, it will be understood that the present heater module may be employed in other applications requiring heated fluid, such as any cleaning system used to clean any vehicle window, i.e., the windshield, rear backlight, or side windows, as well as cleaning systems for vehicle mirrors, camera, lenses, or sensor covers, etc.

0056As is conventional, a vehicle window <b>12</b>, such as a windshield, rear backlight or window, etc., has one or more fluid delivery devices, such as spray nozzles <b>14</b> located in a position to dispense or spray a pattern <b>16</b> of wash fluid onto the exterior surface of the window <b>12</b>. The dispersion of the wash fluid <b>16</b> is usually in conjunction with activation of a windshield wiper <b>18</b> over the window <b>12</b>.

0057The wash fluid <b>16</b> is supplied from a fluid source, such as a reservoir or container <b>20</b>. The fluid in the reservoir <b>20</b> is pumped to the nozzle(s) <b>14</b> by means of a pump <b>22</b> usually located in close proximity or attached to the reservoir <b>20</b>.

0058As is conventional, an on/off switch <b>24</b>, which may be mounted on a vehicle steering column stalk switch, is supplied with power from the vehicle battery <b>26</b> and enables the vehicle driver to control the on or off operation of the wash pump <b>22</b>.

0059According to the invention, the wash fluid pumped from the reservoir <b>20</b> to the spray nozzles <b>14</b> is heated from ambient temperature to a predetermined higher temperature, such as about 65° C. to about 70° C., by example only, by the heater module <b>10</b>. A suitable control circuit or controller <b>28</b> is provided for controlling the operation of the heater elements in the heater module <b>10</b>. The controller <b>28</b> is also supplied with electric power from the vehicle battery <b>26</b>. The controller <b>28</b> is activated by a “on” signal from the vehicle ignition <b>30</b> so as to heat the fluid contained within the flow paths in the heater module <b>10</b>, as described hereafter, whenever the vehicle ignition is in an “on” state.

0060An optional on/off switch <b>25</b> may be connected between the battery <b>26</b> and the controller <b>28</b> to provide on and off operation for the entire heater system by disconnecting power to the controller <b>28</b>. This enables the heater system to be activated or remain in an inactive state at the selection of the vehicle driver. As described hereafter, the on/off switch <b>25</b> may also be replaced by a separate input signal to the controller <b>28</b> from an external signal source, such as a vehicle body controller, to provide for selective deactivation of the heater module <b>10</b> under certain circumstances, such as a thermal event, low battery power, etc.

0061Referring now to <figref idref="DRAWINGS">FIGS. 2–14</figref>, there is depicted one aspect of the heater module <b>10</b> according to the present invention.

0062The heater module <b>110</b> includes a heat exchange mass or body <b>140</b> formed of a suitable high thermally conductive material. Although the mass <b>140</b> is described as being formed of die-cast, molded, or cast or machined aluminum, other materials, either homogeneous or nonhomogeneous, may also be employed. For example, the mass <b>40</b> can be formed of alumina particles, ceramic materials, etc.

0063The use of molding or casting techniques enables highly thermally conductive and moldable materials to be employed for the thermal mass <b>140</b>. For example, the mass <b>40</b> may be formed of a high thermally conductive ceramic material, such as aluminum nitride, boron nitride, magnesium oxide, etc., by example only, which can be molded or cast into the shape of the thermal mass <b>140</b> described hereafter and shown in <figref idref="DRAWINGS">FIGS. 2–14</figref>. The use of ceramic material forms a compact, dense mass of low porosity which provides the desired high thermal conductivity between the heater elements mounted in the mass, the mass itself and the fluid flowing through the mass.

0064When a casting process is employed, the heat transfer rate and/thermal conductivity of the material forming the thermal mass <b>140</b> can be improved when a solid, low porosity material is utilized. Material processing methods, such as squeeze casting, thixocasting, rhiocasting, machining of a solid mill block, etc., can be advantageously employed since such processing methods remove or minimize the porosity or voids for the final formed mass. This enables the thermal conductivity of the thermal mass <b>140</b> to be significantly increase.

0065The thixocasting and rhiocasting processes as described in U.S. Pat. Nos. 6,311,759; 6,372,063; 6,200,396; 5,968,292; and 5,803,154, by way of example, the contents of which are incorporated herein by reference, generally utilize semi-solid materials where a precursor material of a suitable aluminum or other highly thermally conductive material which has been formed with a gobular a-AL phase and cooled into a slug, is placed in a heating device, heated into the semi-solid region between the solidus and liquidus temperatures and then injected or poured into a casting mold.

0066The end result of these processes is a dense mass with low porosity or void space. The lower porosity or void space contributes to a higher thermal conductivity since air normally trapped within such voids or interstices reduces the thermal conductivity of the entire mass due to its insulating properties.

0067For example, the heat transfer rate material effect for a standard casing of 380 aluminum has a thermal conductivity of approximately 96.2 W/m° C. compared to a pored rhiocast or thixocasting with a thermal conductivity of approximately 161W/m° C. using 356/357 aluminum.

0068When an application economically allows the use of a more expensive aluminum material, the resulting heat transfer rate material effect of a thixo or rhiocast material can reach approximately 228 W/m° C.

0069A thermal mass, similar to the thermal mass <b>140</b>, with a different shape or cross-section can also be formed of various materials, such as aluminum, ceramics and poltruded carbon materials by extrusion. Although it may be difficult to extrude the thermal mass <b>140</b>, extrusion of the above mentioned highly thermal conductive materials may be suitable for other thermal mass designs, such as that shown in <figref idref="DRAWINGS">FIGS. 17–29</figref>.

0070Regardless of which of the above mentioned materials and processing techniques are used to form the thermal mass <b>140</b>, the present invention provides a thermal mass <b>140</b> with low porosity and low internal void and interstitial spaces thereby providing the thermal mass <b>140</b> with a high thermal conductivity for high heat transfer between the heating elements through the thermal mass <b>140</b> to the fluid flowing through the channels in the thermal mass, as described hereafter.

0071The mass <b>40</b>, as described in greater detail hereafter, includes a fluid flow path between an inlet <b>42</b> and an outlet <b>44</b>. The inlet and outlet <b>42</b> and <b>44</b>, respectively, each receives a fitting <b>46</b> for receiving a fluid sealed connection to a fluid flow conduit, element or tube, not shown. The inlet <b>42</b> will be connected to receive the pump output from the window wash fluid reservoir <b>20</b>; while the outlet <b>44</b> will be connected to the spray nozzle(s) <b>14</b>.

0072As vehicles typically have several spray nozzles <b>14</b>, usually one for each of the two windshield wipers, and at least one nozzle <b>14</b> for the rear backlight or rear window wiper, it will be understood that the following description of a single heater module <b>10</b> for heating all of the fluid discharge from the fluid reservoir <b>20</b> will encompass multiple parallel paths, each containing a separate heater module, for heating fluid from the reservoir <b>20</b> for each different nozzle <b>14</b>.

0073The heat exchange mass <b>40</b> is disposed within an enclosure or housing formed by a first cover <b>50</b> and a second mating cover <b>52</b>. The first and second covers <b>50</b> and <b>52</b> have complementary mating edges. The first cover <b>50</b> has a major wall surface <b>54</b> and a surrounding peripheral lip <b>60</b>.

0074A necked-down end portion <b>64</b> is formed in the first cover <b>50</b>, and forms a tubular extension from one portion of the major wall surface <b>54</b>. The necked-down portion <b>64</b> forms an enclosure for receiving a connector assembly <b>70</b> which provides electrical signals and power to the heating element(s) mounted in the joined first and second covers <b>50</b> and <b>52</b> and to a circuit board, described in detail hereafter.

0075The second cover <b>52</b> also has a major wall surface <b>56</b> and a surrounding peripheral lip <b>62</b> projecting therefrom. The peripheral lip <b>62</b> surrounds the entire periphery of the second major wall surface <b>56</b>.

0076The first and second covers <b>50</b> and <b>52</b> are fixedly joined together, after the thermal mass <b>40</b> and the connector assembly <b>70</b> has been disposed within the first and second covers <b>50</b> and <b>52</b> by suitable means, such as by heat, sonic or vibration welding. By example, a peripheral groove <b>76</b> projects at least partially around the entire edge of the peripheral lip <b>60</b>. The groove <b>76</b> receives a mating projection <b>77</b> extending around the peripheral lip <b>62</b> of the second cover <b>52</b>. The projection <b>77</b> and groove <b>76</b> are fixedly and sealingly joined together by welding to fixedly join the covers <b>50</b> and <b>52</b> together.

0077Locating means are provided for locating and fixing the thermal mass <b>40</b> to the first and second covers <b>50</b> and <b>52</b>. At least one and preferably a pair of circumferentially spaced slots <b>79</b> and <b>81</b>, are formed on webs <b>83</b> extending between two bosses receiving the threaded fasteners on the mass <b>40</b>. The slots <b>79</b> and <b>81</b> receive projections <b>85</b> and <b>87</b> carried on flanges in the first and second covers <b>50</b> and <b>52</b> at circumferentially spaced locations complementary to the location of the slots <b>79</b><b>81</b> in the mass <b>40</b>. The projections <b>85</b> and <b>87</b> are welded together when the covers <b>50</b> and <b>52</b> are subjected to a sonic, heat or vibration welding process. In this matter, the thermal mass is fixedly positioned within the covers <b>50</b> and <b>52</b> when the covers <b>50</b> and <b>52</b> are themselves joined together.

0078A pair of seal elements <b>71</b> and <b>72</b>, each having a ring shape with another edge substantially the same as the peripheral shape of the heat exchange mass <b>40</b> are disposed on opposite surfaces of the heat exchange mass <b>40</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. The seal members <b>71</b> and <b>72</b> are formed of a high thermal resistant, insulating material. The seal members <b>71</b> and <b>72</b> seal the periphery of the heat exchange mass <b>40</b>.

0079Upper and lower closures or plates <b>73</b> and <b>74</b>, each also having a shape complimentary to the shape of the heat exchange mass <b>40</b>, are disposed in contact with the upper and lower seals <b>71</b> and <b>72</b>, respectively, and fixed thereto by suitable fastening means, such as nuts and bolts <b>75</b>, which extend through apertures in each of the upper and lower plates <b>73</b> and <b>74</b>, and peripherally located bores in heat exchange mass <b>40</b>. The solid peripheral edges of the plates <b>73</b> and <b>74</b> and the mating peripheral edges of the heat exchange mass <b>40</b> trap the seals <b>71</b> and <b>72</b> there between to seal the joint between the plates <b>73</b> and <b>74</b> and the mass <b>40</b>. The upper and lower plates <b>73</b> and <b>74</b> are formed of a good thermally conductive material, such as aluminum.

0080As shown in detail in <figref idref="DRAWINGS">FIGS. 6–11</figref>, the heat exchange mass <b>40</b> has a solid cubical shape formed of a first major surface <b>80</b>, a second opposed major surface <b>82</b>, and four sidewall portions <b>84</b>, <b>86</b>, <b>88</b> and <b>90</b>, interconnecting the first and second surfaces <b>80</b> and <b>82</b>.

0081A plurality of bores <b>92</b>, <b>94</b> and <b>96</b> are formed in the body <b>40</b> and project inwardly from the sidewall <b>84</b>. The bores <b>92</b>, <b>94</b> and <b>96</b> are each adapted for receiving one generally cylindrical heater element. As partially shown in <figref idref="DRAWINGS">FIG. 11</figref>, each bore <b>92</b>, <b>94</b> and <b>96</b> extends through the solid central portion of the mass <b>40</b> so as to be completely surrounded by the solid material of the mass <b>40</b>. This defines the mass <b>40</b> as a heat source after receiving heat from the heater elements mounted in each bore <b>92</b>, <b>94</b> and <b>96</b>.

0082In the invention, the heater elements may be formed of “calrod”. Although different materials may be used, one example of a calrod construction is a Nichrome wire inside of a stainless steel sheath.

0083By way of example only, at least one and preferably a plurality, i.e., two or three or more individual heater elements <b>100</b>, <b>102</b> and <b>103</b>, are disposed in the bores <b>92</b>, <b>94</b> and <b>96</b>, respectively. The function of the one or more heater elements, such as heater elements <b>100</b>, <b>102</b> and <b>103</b> will be described hereafter in conjunction with a description of the operation of the heater module <b>10</b>.

0084As seen in <figref idref="DRAWINGS">FIGS. 4 and 7</figref>, one end <b>104</b>, <b>106</b> and <b>107</b> of each heater element <b>100</b>, <b>102</b> and <b>103</b>, respectively, projects outwardly through the sidewall <b>84</b> of the body <b>40</b>. The ends <b>104</b>, <b>106</b> and <b>107</b> of the heater elements <b>100</b>, <b>102</b> and <b>103</b>, respectively, each have individual terminals <b>108</b> extending therefrom and joined thereto by soldering, welding, etc., for connection to mating sockets or contact spring mounted on a printed circuit board <b>150</b>, itself mounted by means of fasteners, i.e., screws, rivets, or adhesives, etc., to an exterior surface of the plate <b>73</b>. Conductive traces in the printed circuit board <b>150</b> are connected to sockets or contacts which receive the terminals <b>108</b>. Two of the connector terminals <b>70</b> are soldered to the printed circuit board <b>150</b> to receive power, ground and control signals from the vehicle electrical system.

0085As shown in <figref idref="DRAWINGS">FIGS. 9 and 10</figref>, the thermally conductive mass <b>40</b> includes a fluid flow channel or path which extends from the inlet <b>42</b> to the outlet <b>44</b>. The fluid flow path is, by example, a labyrinthian path formed of a first fluid flow path portion <b>130</b> and a second fluid flow path or channel <b>132</b> which are connected at a generally centrally disposed bore <b>134</b>. The first fluid flow channel <b>130</b> has a generally spiral shape formed of alternating straight and arcuate sections which alternately create laminar and turbulent flow of the fluid passing through the first flow channel <b>130</b> to maximize the heat absorption of the fluid from the adjoining walls of the mass <b>40</b>. Further, the first fluid flow channel <b>130</b> has an inward directed spiral shape from the inlet <b>42</b> to the bore <b>134</b> to minimize temperature differential between adjoining portions of the spiral shaped first flow channel <b>130</b>.

0086As shown in <figref idref="DRAWINGS">FIG. 10</figref>, the second fluid flow channel <b>132</b> has a substantially identical spiral shape. However, fluid flow through the second fluid flow channel <b>132</b> is in an outward spiral direction from the bore <b>134</b> to the outlet <b>44</b>.

0087Thus, fluid flow through the first and second flow channels <b>130</b> and <b>132</b> starts from the inlet <b>44</b> then continues in a spirally inward directed manner through the first flow channel <b>130</b> to the central passage or bore <b>134</b>. Upon exiting the central passage <b>134</b> into the second flow channel <b>132</b>, fluid flow progresses in an outward spiral direction through the second flow channel <b>132</b> to the outlet <b>44</b>.

0088In operation, the heater module <b>40</b> will be interconnected in the vehicle wash fluid flow lines between the pump <b>22</b> and the spray nozzle(s) <b>14</b> as shown in <figref idref="DRAWINGS">FIG. 1</figref>. The external connector is then connected to the connector housing <b>70</b> to provide electric power from the vehicle battery <b>26</b> and the controller <b>28</b> to the heater elements <b>100</b>, <b>102</b> and <b>103</b>, in the heat exchange body <b>40</b>.

0089Assuming that the first and second fluid flow channels <b>130</b> and <b>132</b> in the body <b>40</b> are filled with fluid, when the controller <b>28</b> activates the heater elements <b>100</b>, <b>102</b> and <b>103</b>, the heater elements <b>100</b>, <b>102</b> and <b>103</b> will begin radiating heat which will immediately raise the temperature of the entire surrounding portion of the heat exchange body <b>40</b>. Heat from the body <b>40</b> will, in turn, be radiated to and absorbed by the fluid disposed in the first and second flow channels <b>130</b> and <b>132</b>.

0090The straight and arcuate portions of the first and second fluid flow channels <b>130</b> and <b>132</b> create alternating turbulent and laminar flow regions in the fluid flowing through the mass <b>40</b> which causes movement of the fluid in the first and second flow channels <b>130</b> and <b>132</b> bringing all molecules in the fluid in contact with the wall of the body <b>40</b> forming the first and second flow channels <b>130</b> and <b>132</b> to efficiently absorb the maximum amount of heat possible. This causes the temperature of the fluid to be quickly raised from ambient temperature at the inlet <b>42</b> to approximately 160° F.–170° F. at the outlet <b>44</b> in approximately sixty seconds.

0091The fluid in the first and second fluid flow channels <b>130</b> and <b>132</b> removes or absorbs heat from the thermal mass <b>40</b> thereby increasing the fluid temperature by physical contact with the mass <b>40</b>. The heater elements <b>100</b>, <b>102</b> and <b>103</b> maintain the heat of the thermal mass <b>40</b> at a predetermined temperature thereby preventing hot spots from occurring in the fluid. Normally, hot spots would occur when the fluid comes in direct contact the heater elements <b>100</b>, <b>102</b> and <b>103</b>. Fluid which is not in physical contact with the heater elements <b>100</b>, <b>102</b> and <b>103</b> passes the heater elements <b>100</b>, <b>102</b> and <b>103</b> by and does not absorb heat. By heating the thermal mass <b>40</b>, the physical hot contact area is increased along with an increase in heat transfer efficiency. This requires less energy to heat the same volume of fluid.

0092Although a single heater element <b>100</b> may be employed as the heat source in the body <b>40</b>, multiple heater elements, with two or three heater elements, <b>100</b>, <b>102</b> and <b>103</b>, being described by way of example only, have been found to be most advantageous. The controller <b>28</b> can activate all of the plurality of heater elements <b>100</b>, <b>102</b> and <b>103</b> upon receiving a first command to dispense heated wash fluid onto the windshield <b>12</b>. This generates a maximum amount of heat to the body <b>40</b> to immediately and quickly raise the temperature of the body <b>40</b> high enough to transfer sufficient heat to the fluid in the fluid flow channels <b>130</b> and <b>132</b> to raise the temperature of the fluid to the desired discharge temperature of about 65° C. to about 70° C. The multiple heater elements <b>100</b>, <b>102</b> and <b>103</b> can remain in an activated state by the controller <b>28</b> if immediate and successive commands from the on/off switch <b>24</b> are supplied by the vehicle driver to supply additional charges of fluid onto the windshield <b>12</b>.

0093At the completion of the fluid dispensing operation, and during other periods of non-fluid dispensing while the vehicle engine is running or the engine is running and a dashboard mounted switch, for example, is activated, the controller <b>28</b> can cyclically activate one or more of the heater elements, such as heater element <b>100</b>, to maintain the temperature of the fluid in the first and second flow channels <b>130</b> and <b>132</b> at an elevated temperature for immediate discharge onto the windshield <b>12</b> when activated by the on/off switch <b>24</b>. This minimizes electrical power requirements on the vehicle battery <b>26</b>.

0094Although the controller <b>28</b> can provide separate switchable signals to each of the heater elements <b>100</b>, <b>102</b> and <b>103</b>, in order to control each heater element <b>100</b>, <b>102</b> and <b>103</b> separately under program or logic control, one alternate approach includes a bi-metal element or a switch mounted between the power connections to one terminal <b>108</b> and each of the other terminals <b>108</b> connected to the additional heater elements <b>102</b> and <b>103</b>. The bi-metal element can be set to open at a predetermined temperature, such as 50° C., thereby deactivating the associated heater element. This enables the additional heater elements <b>102</b> and <b>103</b>, for example, to remain deactivated until a high heat requirement is initiated.

0095Although the following description of the use of high amperage switching devices known as MOSFETs, are used as part of the controller <b>28</b> and to provide the necessary high current, typically 50 amps at 12 volts, to the heating elements <b>100</b>, <b>102</b> and <b>103</b> in the thermal mass <b>40</b>, other high amperage switching devices may also be employed. Any number of MOSFETs <b>156</b> can be mounted in any configuration on the printed circuit board <b>150</b>.

0096A plurality of bores <b>158</b> are optionally formed through the printed circuit board <b>150</b>. The bores <b>158</b> improve heat flow between the switching devices on the printed circuit board (PCB) <b>150</b> and the underlying first plate <b>73</b>.

0097A temperature sensor <b>159</b>, such as a PTC, is mounted on the printed circuit board <b>150</b>, typically over or adjacent to the bores <b>158</b>. The temperature sensor <b>159</b> measures the temperature of the printed circuit board <b>150</b> and provides a temperature proportional signal to the controller <b>28</b> which is used by the controller <b>28</b> to control the on/off cycle of the heater elements <b>100</b>, <b>102</b> and <b>103</b>.

0098To further enhance transfer of the heat generated by the MOSFETs <b>156</b> to the first plate <b>140</b>, a highly conductive pad or plate <b>161</b>, hereafter referred to as a sill pad <b>161</b>, is interposed in contact between the printed circuit board <b>150</b> and the first plate <b>23</b> as shown in <figref idref="DRAWINGS">FIGS. 3</figref>, <b>8</b> and <b>9</b>. The sill pad <b>161</b> typically has a planar shape and dimensions to extend over at least a portion of the first plate <b>73</b>. The pad <b>161</b> isolates stray electrical currents to negative ground through the screws <b>75</b>, provides a positive contact between the MOSFETs and the thermal mass <b>40</b>, and stabilizes heat loss through the adjacent cover by maintaining the temperature of the plate <b>73</b> at a higher temperature to thereby create a lower temperature differential or gradient with respect to the thermal mass <b>40</b>.

0099The sill pad <b>161</b> preferably has a higher thermal conductivity than the thermal conductivity of the plate <b>73</b> to efficiently draw heat generated by the MOSFETs <b>156</b> to the plate <b>73</b> thereby maintaining the temperature of the plate <b>73</b> at an elevated temperature. This elevated temperature of the plate <b>73</b> is higher than the normal temperature of the plate <b>73</b> caused by heat escaping from the sides of the thermal mass <b>40</b> around the seals <b>71</b> and <b>72</b>.

0100It is known that during sub-freezing temperatures, wash fluids which are formed substantially of water are subject to freezing. The expansion of the frozen or semi-frozen fluid causes pressure to be exerted against the surrounding components of the heater module <b>10</b> which could lead to leaks or to the complete destruction of the heater module <b>10</b>.

0101As shown in <figref idref="DRAWINGS">FIGS. 3</figref>, <b>5</b> and <b>11</b>–<b>14</b>, a fluid expansion means <b>160</b> is carried in the heater module <b>10</b> for reversibly allowing expansion of the fluid in the fluid flow path when the fluid changes phase from a liquid to a substantially solid state. The fluid expansion means, in one aspect of the present invention, is in the form of a thin compressive member such as a generally planar member, formed of a closed cell foam.

0102One example of a suitable material which could be used to form the fluid expansion means is a closed cell polyolefin foam sold by Voltek, division of Sekisui America Corp., as product number VOLARA type LM. Another possible material is a polyvinyl chloride allied foam, trade name C/3002 or C-2301 from Specialty Composites Division Cabot Safety Corp., Indianapolis, Ind. 46254.

0103The fluid expansion means <b>160</b> has sufficient rigidity under normal fluid operating pressures in the mass <b>40</b> to resist compression. The fluid expansion means or member <b>160</b> is disposed over an inner edge of each of the seals <b>71</b> and <b>72</b> on both sides of the thermal mass <b>30</b> and has a substantial center portion facing and exposed to the fluid through the open ends of the channels in the thermal mass <b>40</b>. The fluid expansion member <b>160</b> has sufficient rigidity to resist expansion or compression under the normal operating pressures of the fluid in the heater module <b>10</b>. However, at the substantially higher forces exerted by freezing and expansion of the fluid in the channels, the member <b>160</b> is capable of compression as shown in phantom in <figref idref="DRAWINGS">FIGS. 12 and 13</figref> to allow space for the expanded frozen or semi-frozen fluid.

0104The fluid expansion member <b>160</b> has shape memory so as to return to its normally generally planar shape, completely filling an internal cavity <b>162</b> formed in an enlarged bulge in each cover <b>71</b> and <b>73</b>.

0105The fluid expansion member <b>160</b> is compressed by the fastening on the plate <b>73</b> and <b>74</b> to the mass to expand slightly into the channels in the mass <b>40</b> and into substantial contact with the surfaces of the thermal mass <b>40</b> to close off the open ends of each of the channels in the fluid flow path through the thermal mass <b>40</b>.

0106As shown in <figref idref="DRAWINGS">FIG. 14</figref>, the fluid expansion member <b>160</b> has additional features to facilitate its use in the heater module <b>10</b>. A pair of open ended recesses <b>164</b> and <b>166</b> are formed along one edge of the fluid expansion member <b>160</b>. The recesses <b>164</b> and <b>166</b> overlay a portion of the underlying fluid flow channel of the thermal conductive mass <b>40</b> to permit a small amount of the fluid in the fluid flow channel to flow through the recesses <b>164</b> and <b>166</b> against the inside surface of the plate <b>73</b> or <b>74</b>. The high power consuming electronic switching devices, such as the MOSFETs <b>156</b>, are located immediately opposite an enlargement in the plate <b>73</b>. The switching devices <b>156</b> are cooled by the flow of water so as to maintain the switching devices <b>156</b> at a nominal operating temperature. Additional apertures <b>168</b> and <b>170</b> are formed in an intermediate portion of the thermal expansion member <b>160</b> for a similar purpose to allow fluid flow through the channels in the thermal conductive mass to flow against an inner surface of the adjacent plate <b>73</b> to remove heat from the switching devices <b>156</b> located immediately there over on the circuit board <b>150</b>.

0107An additional open-ended recess <b>172</b> is formed on another edge portion of the thermal expansion member <b>160</b>. The recess <b>172</b> underlies the position of the thermal temperature sensor <b>159</b> mounted on the circuit board <b>150</b>. Fluid flow through the recess <b>172</b> provides a more accurate temperature measurement by the temperature sensor <b>159</b> since it is closer to the fluid flowing through the channels in the thermal mass <b>40</b>.

0108In another aspect of the fluid expansion means <b>200</b> shown in <figref idref="DRAWINGS">FIG. 16</figref>, the fluid expansion means <b>200</b> is configured to eliminate the seal <b>71</b> and <b>72</b>. The peripheral edge portion <b>202</b> of the fluid expansion means or element is compressed when the corresponding plate <b>73</b> or <b>74</b> is securely fixed to the thermal mass <b>40</b> by means of the fasteners <b>75</b>. Alternately, the peripheral edge portion <b>202</b> of the fluid expansion means <b>200</b> can be heat and pressure compressed to a smaller thickness than the central portion of the fluid expansion element <b>200</b>.

0109In an optional modification shown in <figref idref="DRAWINGS">FIG. 15</figref>, the fluid expansion means <b>180</b> is formed by the seal members <b>182</b> and <b>184</b> having a solid shape over their entire surface area. At least one of the thus formed seal members <b>182</b> and <b>184</b> is formed with sufficient rigidity to resist expansion when exposed to the normal pressures of fluid flowing through the open ended channels in the thermal mass <b>40</b>. However, any of the seal members <b>182</b> and <b>184</b> are capable of expansion into an interior cavity or chamber <b>186</b> formed in the enlarged portion of the plate <b>73</b> between the seal <b>182</b> and the inner surface of the plate <b>73</b> to accommodate the expanded frozen or semi-frozen fluid from the mass <b>40</b>. When the fluid subsequently changes phase back to a liquid state, the seal members <b>182</b> and <b>184</b> will assume their original shape wherein each of the seal members <b>182</b> and <b>184</b> is disposed in contact with the open ends of the channels closing off the open end of the channels in the fluid flow path to maintain the desired labyrinthian flow of fluid through the thermal mass <b>40</b> as described above.

0110Referring now to <figref idref="DRAWINGS">FIG. 17</figref>, there is depicted another aspect of a heater apparatus or module <b>310</b> constructed in accordance with the teachings of the present invention. Although the following use of the heater module <b>310</b> of the present invention is described in conjunction with a vehicle window wash system as shown in <figref idref="DRAWINGS">FIG. 1</figref>, it will be understood that the present heater module may be employed in other applications requiring heated fluid, such as any cleaning system used to clean any vehicle window, i.e., the windshield, rear backlight, or side windows, as well as cleaning systems for vehicle mirrors, camera, lenses, or sensor covers, etc.

0111Referring back to <figref idref="DRAWINGS">FIG. 1</figref>, the wash fluid <b>16</b> is supplied from a fluid source, such as a reservoir or container <b>20</b>. The fluid in the reservoir <b>20</b> is pumped to the nozzle(s) <b>14</b> by means of a pump <b>22</b> usually located in close proximity or attached to the reservoir <b>20</b>.

0112As is conventional, an on/off switch <b>24</b>, which may be mounted on a vehicle steering column stalk switch, is supplied with power from the vehicle battery <b>26</b> and enables the vehicle driver to control the on or off operation of the wash pump <b>22</b>.

0113According to the invention, the wash fluid pumped from the reservoir <b>20</b> to the spray nozzles <b>14</b> is heated from ambient temperature to a predetermined higher temperature, such as 160° F.–170° F., by example only, by the heater module <b>310</b>. A suitable control circuit or controller <b>28</b> is provided for controlling the operation of the heater elements in the heater module <b>310</b>. The controller <b>28</b> is also supplied with electric power from the vehicle battery <b>26</b>. The controller <b>28</b> is activated by an “on” signal from the vehicle ignition <b>30</b> so as to heat the fluid contained within the flow paths in the heater module <b>310</b>, as described hereafter, whenever the vehicle ignition is in an “on” state.

0114An optional on/off switch <b>25</b> may be connected between the battery <b>26</b> and the controller <b>28</b> to provide on and off operation for the entire heater system by disconnecting power to the controller <b>28</b>. This enables the heater system to be activated or remain in an inactive state at the selection of the vehicle driver. As described hereafter, the on/off switch <b>25</b> may also be replaced by a separate input signal to the controller <b>28</b> from an external signal source, such as a vehicle body controller, to provide for selective deactivation of the heater module <b>310</b> under certain circumstances, such as a thermal event, low battery power, etc.

0115The heater module <b>310</b> is shown in greater detail in <figref idref="DRAWINGS">FIGS. 18–29</figref>. The heater module <b>310</b> includes a housing <b>340</b> formed of a generally cylindrical, tubular sleeve <b>342</b> having a hollow throughbore extending between opposed ends. The sleeve <b>342</b> is formed of a thermal insulating material, such as a foam plastic material, to thermally insulate the high temperature fluids passing through a heat exchange, thermally conductive mass <b>350</b> mounted within the housing <b>340</b>.

0116As shown in <figref idref="DRAWINGS">FIG. 18</figref>, the heat exchange mass or body <b>350</b> is mounted within the sleeve <b>342</b>. The heat exchange mass <b>350</b> is held in position within the sleeve <b>342</b> by a top end cover <b>352</b> and a bottom end cover <b>354</b> both of which are fixedly mounted to opposite ends of the sleeve <b>342</b> by suitable means, such as swagging, welding, threads, etc.

0117As shown in <figref idref="DRAWINGS">FIGS. 18 and 20</figref>, the top end cover <b>352</b> includes an enlarged diameter end flange <b>356</b> at one end and a generally circular sleeve <b>358</b> projecting therefrom to an opposite end. Side tabs <b>360</b> and <b>362</b> project along diametrically opposed portions of the sleeve <b>358</b> and outward from the end of the sleeve <b>358</b> for connection to ridge <b>364</b> on a housing <b>394</b>. The end flange <b>356</b> is adapted to seat against one end of the heat exchange mass <b>350</b> within the interior of the sleeve <b>342</b>. The sleeve <b>358</b> projects axially from the flange <b>356</b> and is adapted to mate with an electric connector housing <b>364</b> and an electric terminal assembly <b>366</b>, both described in greater detail hereafter.

0118A plurality of circumferentially arranged dimples <b>368</b> are formed in the end flange <b>356</b> within the interior of the sleeve <b>358</b>. Interspersed within the dimples <b>368</b> are a plurality of bosses <b>370</b>, with four being shown by way of example only. Each boss <b>370</b> includes a throughbore or aperture <b>371</b> which is adapted to receive a cylindrical heating element <b>372</b> or a ground rod <b>374</b> or a ground lead frame, as described hereafter.

0119As also shown in <figref idref="DRAWINGS">FIGS. 18 and 20</figref>, an inlet port fitting <b>376</b> is also formed in the top end cover <b>352</b>, integrally with the sleeve <b>358</b>, by way of example only. A bore <b>378</b> extends through the fitting <b>376</b> and the end flange <b>356</b>.

0120The heater elements <b>372</b> or the ground rod <b>374</b> may be formed of any suitable heating element. In one aspect, the heater element <b>372</b> are formed of “calrod”. Although different materials maybe used, one example of a calrod construction is a Nichrome wire inside of a stainless steel sheath.

0121As shown in <figref idref="DRAWINGS">FIG. 18</figref>, a flange <b>375</b> is formed on one end of the sheath of each heater element <b>372</b> and ground rod <b>374</b>. The flange <b>376</b> supports a seal element <b>377</b>, such as an O-ring, for sealing the mounting connection between the heater elements <b>372</b> and the ground rod <b>374</b> and the top end cover <b>352</b>.

0122The bottom end cover <b>354</b> is shown in detail in <figref idref="DRAWINGS">FIGS. 18 and 21</figref>. The bottom end cover <b>354</b> has a generally planar wall <b>380</b> with a circular cross-section so as to be fixed to an inner end of the sleeve <b>342</b> as shown in <figref idref="DRAWINGS">FIG. 20</figref>. A plurality of dimples <b>382</b> are formed in a circumferentially spaced, circular arrangement in the wall <b>380</b> of the bottom end cover <b>354</b> and are arranged to project into certain apertures in the heat exchange mass <b>350</b> as will be described in greater detail hereafter. An outlet port or fitting <b>384</b> projects from the wall <b>380</b>. A throughbore <b>386</b> extends through the port or fitting <b>384</b> and the wall <b>380</b> for communication with the interior of the inner sleeve <b>342</b>.

0123The electrical connector housing <b>364</b> is fixed within one end of the inner sleeve <b>342</b>. The connector housing <b>64</b> is formed as an integral, one piece body <b>390</b> of a suitable electrically and thermally insulating plastic as shown in <figref idref="DRAWINGS">FIGS. 18 and 22</figref>. The body <b>390</b> includes a first generally circular end portion <b>392</b> having a key or detent <b>394</b> at one circumferential position. The first end portion <b>392</b> forms an interior recess which surrounds one end of terminal leads <b>401</b>. The terminal leads <b>401</b> are fixedly mounted in the first end portion <b>392</b>, such as through slots formed in a central wall of the first end portion <b>392</b>. One end of the terminal leads <b>401</b>, not shown, is connected to a circuit board <b>366</b>, shown in <figref idref="DRAWINGS">FIG. 19</figref>, containing control circuitry mounted in the interior of the first end portion <b>392</b>.

0124The terminal leads <b>401</b> extend from the second end portion <b>392</b> of the connector housing <b>364</b> to an electrical contact connection with the exposed end of the inner wire portion of each heating element <b>372</b> or ground rod <b>374</b>.

0125A second portion <b>402</b> of the connector housing <b>364</b> has a generally rectangular shape with rounded ends and is connected to the first portion <b>390</b> by a narrow rib <b>404</b> having a plurality of through apertures <b>406</b> formed therein as shown in <figref idref="DRAWINGS">FIG. 23</figref>.

0126Terminal leads <b>400</b>, as shown in detail in <figref idref="DRAWINGS">FIG. 24</figref>, are initially joined by frangible webs <b>408</b> in pairs or groups of three or four leads <b>400</b>. The terminal leads <b>400</b> are mounted through an interior wall in the first end portion <b>392</b> of the connector housing <b>364</b> so that the webs <b>408</b> connecting the terminal leads <b>400</b> together are exposed through the apertures <b>406</b> in the web <b>404</b> as shown in <figref idref="DRAWINGS">FIGS. 23 and 22</figref>. After the terminal leads <b>400</b> are fixedly mounted in the connector housing <b>364</b>, the webs <b>408</b> are separated or broken away from the terminals or leads <b>400</b> to separate each terminal <b>400</b> from the other terminal leads <b>400</b>. The terminal leads <b>400</b> are exposed in the second portion <b>402</b> of the connector housing <b>364</b> and mate with a plug containing complementary sockets for connecting electrical power, ground and external signals to the terminal leads <b>400</b>. The other end of the terminal leads <b>400</b> are mounted in sockets or soldered to terminals on the circuit board <b>366</b> mounted in the first end portion <b>92</b> of the connector housing <b>364</b>.

0127As shown in <figref idref="DRAWINGS">FIG. 18</figref>, at least one and preferably a pair of diametrically opposed latch elements <b>379</b> are formed on the connector housing <b>364</b>. The latch elements <b>379</b> mate with a latch receiver or recess in the top end cover <b>352</b> to latchingly couple the connector housing <b>364</b> to the top end cover <b>352</b> and sandwich the circuit board <b>366</b> between adjacent end flanges of the connector housing <b>364</b> and the top end cover <b>352</b>.

0128As shown in <figref idref="DRAWINGS">FIG. 18</figref> and in detail in <figref idref="DRAWINGS">FIGS. 26–29</figref>, the heat exchange mass <b>350</b>, also hereafter referred to as a “stack”, is formed of a plurality of individual heat exchange elements or lamina <b>420</b> as shown in <figref idref="DRAWINGS">FIG. 25</figref>. Each lamina <b>420</b> has the same identical shape, such as a circular cross-section, so as to fit tightly within the inner diameter of the inner sleeve <b>342</b>, and is formed as a thin plate of a suitable highly thermal conductive material, such as aluminum, ceramic, pressed alumina particles, etc.

0129Each lamina <b>420</b> may be formed by the molding or casting processes described above for the thermal mass <b>140</b>. That is, casing or molding as a semi-solid material by spin casting, thixocasting or rhiocasting, will form each lamina <b>420</b> with the lowest porosity for maximum thermal conductivity. Each lamina <b>420</b> may also be molded from poltruded carbon materials, as well as a metal such as aluminum.

0130The use of an extrusion process is ideally suited for forming each lamina <b>420</b> individually or as one continuous block or mass. The block or mass may be cut to length to provide a predetermined heat transfer capability for the fluid system. In additional, using known extrusion techniques, it is possible to form the helical flow paths in the mass as the mass exits the extrusion die by rotating the extrusion die itself or the extrudate discharge from the extrusion die during extrusion.

0131As shown in <figref idref="DRAWINGS">FIGS. 25 and 26</figref>, each identically constructed lamina <b>420</b>, including lamina <b>420</b><i>a</i>, <b>420</b><i>b </i>and <b>420</b><i>c </i>are provided with a plurality of inner apertures <b>422</b> which are in a generally circular arrangement at a defined circumferential, center to center spacing denoted by reference number <b>424</b>. This spacing <b>424</b> is hereafter used to define a “helical offset”.

0132The inner diameter of the apertures <b>422</b> is sized to slidably receive the cylindrical heater elements <b>372</b> or the ground rod <b>374</b> in any aperture <b>422</b>. Thus, despite any helical or angular offset between adjacent lamina <b>420</b><i>a</i>, <b>420</b><i>b </i>and <b>420</b><i>c</i>, as described hereafter, either in a single step, a double step, a triple step, a quintuple step helical offset, etc., the apertures <b>422</b> in each lamina <b>420</b><i>a</i>, <b>420</b><i>b</i>, <b>420</b><i>c</i>, etc., will remain longitudinally coaxially aligned with the apertures <b>422</b> in the adjacent lamina <b>420</b><i>a</i>, <b>420</b><i>b </i>and <b>420</b><i>c</i>. This enables the apertures <b>422</b> in the entire heat exchange mass or stack <b>350</b> to form elongated, axial throughbores <b>426</b> seen in <figref idref="DRAWINGS">FIG. 27</figref>, which slidably receive one of the heater elements <b>372</b> or the ground rod <b>374</b>. The heater elements <b>372</b> and the ground rod <b>374</b>, once inserted into the bores <b>426</b> in the heat exchange stack <b>350</b> , will also retain the lamina <b>420</b> in the desired helical offset arrangement as defined hereafter.

0133Referring back to <figref idref="DRAWINGS">FIGS. 25 and 26</figref>, each lamina <b>420</b>, <b>420</b><i>a</i>, <b>420</b><i>b</i>, <b>420</b><i>c, </i>etc., also includes a plurality of outer radially disposed apertures arranged in two groups of apertures including an inner group of apertures <b>430</b> and an outer group of apertures <b>432</b>. It will be understood that this arrangement is by example only as the apertures <b>430</b> or <b>432</b> can be arranged in other configurations. However, the circumferentially spacing between the equal radially spaced inner apertures <b>430</b> and the different but still equal radially spaced outer group of apertures <b>432</b> disposed at a greater radially spacing then the inner group of apertures <b>430</b> provide an optimum number of flow paths through the stack <b>350</b> for heat exchange efficiency with fluid flowing through the stack <b>350</b> as described hereafter. As shown in <figref idref="DRAWINGS">FIGS. 25 and 26</figref>, the apertures <b>430</b> and <b>432</b> alternate around the circumference of each lamina <b>420</b>.

0134As shown in <figref idref="DRAWINGS">FIGS. 26 and 28</figref>, for a single step helical offset, the lamina <b>420</b> are arranged in stack including lamina <b>420</b><i>a</i>, <b>420</b><i>b</i>, <b>420</b><i>c</i>, etc., with each lamina rotatably offset from one adjacent lamina, as viewed from the top end cover <b>352</b> in <figref idref="DRAWINGS">FIG. 27</figref>, by one circumferential center or helical offset to center spacing <b>424</b> of the apertures <b>422</b> which receive the heater elements <b>372</b>. This provides a helically extending, stepwise flow path denoted by reference number <b>440</b> for the inner series of apertures <b>430</b> and reference number <b>442</b> for the outer series of apertures <b>432</b>. This single step helical offset example shown in <figref idref="DRAWINGS">FIG. 28</figref> significantly increases the surface area of the stack which is exposed through each helically extending bore or fluid flow path <b>440</b> and <b>442</b> and provides for greater heat absorption by the fluid flowing through the flow paths <b>440</b> and <b>442</b> due to the increased contact time between the fluid and the surfaces of the lamina <b>420</b> forming the fluid flow paths <b>440</b> and <b>442</b>, etc., as compared to an arrangement where all of the apertures <b>430</b> are axially aligned with like apertures <b>130</b> in adjacent lamina <b>420</b> and the apertures <b>432</b> are likewise axially aligned with like apertures <b>432</b> in the adjacent lamina <b>420</b>.

0135Each fluid flow path, such as fluid flow path <b>440</b> and <b>442</b>, helically extends between the inlet chamber formed between one surface of the top end cover <b>352</b> and one end of the stack <b>350</b> and the outlet chamber formed between the bottom end cover <b>354</b> and the opposed end of the stack <b>350</b>. Depending on the length of the stack <b>350</b>, the flow paths <b>440</b> and <b>442</b>, for example, can extend approximately 540° around a longitudinal axis of the stack <b>350</b> between the inlet and the outlet. This extending length, as compared to a straight throughbore or flow path, greatly increases the contact time between the fluid and the surrounding surfaces of the stack <b>350</b> so as to enable greater quantities of heat to be absorbed from the lamina <b>420</b> by the fluid to increase the efficiency of the heater module <b>310</b> of the present invention.

0136Other features of the apertures <b>430</b> and <b>432</b> can be more clearly understood by referring to <figref idref="DRAWINGS">FIG. 29</figref>. As shown therein, the outer apertures <b>432</b> denoted in <figref idref="DRAWINGS">FIG. 29</figref> as outer apertures <b>432</b><i>a </i>and <b>432</b><i>b </i>for two different lamina <b>420</b><i>a </i>and <b>420</b><i>b</i>, are disposed at a first radius R₁. The apertures <b>430</b><i>a </i>and <b>430</b><i>b </i>in the lamina <b>420</b><i>a </i>and <b>420</b><i>b </i>are disposed at a different, smaller radius R₂. Similarly, the diameter or maximum cross-section of the outer apertures <b>432</b><i>a </i>and <b>432</b><i>b </i>is greater than the diameter or maximum cross-section of the inner disposed apertures <b>430</b><i>a </i>and <b>430</b><i>b</i>. However, the helical offset which results in a step wise circumferential advance from the aperture <b>430</b><i>a </i>in the adjacent lamina <b>420</b><i>a </i>and between the aperture <b>432</b><i>b </i>in the lamina <b>420</b><i>b </i>from the aperture <b>432</b><i>a </i>in the lamina <b>420</b><i>a </i>still results in the same cross-section area in each of the bores <b>430</b> and <b>432</b> formed by the inner apertures <b>430</b> (<b>430</b><i>a</i>, <b>430</b><i>b</i>, etc.,) and the outer apertures <b>432</b> (<b>432</b><i>a</i>, <b>432</b><i>b</i>, etc.,). This forms equal cross-sectional flow paths and equal resistance to fluid flow in each of the helical bores <b>440</b> and <b>442</b> thereby creating equal flow rates through each of the bores <b>440</b> and <b>442</b> throughout the entire heat exchange stack <b>350</b>.

0137In operation, with the heater module <b>310</b> assembled together as described above, a fluid supply from the pump <b>322</b> can be attached to the inlet fitting <b>376</b>. Similarly, another conduit connected to the spray nozzle(s) <b>314</b> can be connected to the outlet <b>384</b>. When the ignition <b>326</b> is turned “on”, the controller <b>28</b> supplies power to the one or more heater elements <b>372</b> disposed in certain of the inner bores <b>422</b> in the stack <b>350</b>. To quickly raise the temperature of fluid contained within the bores <b>440</b> and <b>442</b>, all of the heater elements <b>372</b> can be activated. Once the temperature of the fluid in the stack <b>350</b> has reached a predetermined temperature suitable for discharge through the nozzle(s) <b>14</b>, a thermocouple, not shown, connected to the stack <b>350</b> or situated in one of the bores <b>440</b> and <b>442</b> or adjacent the bottom end cover <b>384</b> will supply a feedback signal to the controller <b>328</b> which will then deactivate one or more of the heater elements <b>372</b> until only one heater element <b>372</b> is turned on continuously or cyclically to maintain the fluid temperature at the desired discharge temperature, such as 160° F.–170° F. Alternately, if more time is available to heat the fluid, only one or two of the heater elements <b>374</b> are activated.

0138When the vehicle driver activates the on/off switch <b>324</b>, the pump <b>322</b> will be activated to pressurize the fluid delivery line through the heater module <b>310</b> to the spray nozzle(s) <b>14</b>. This will cause the fluid in the stack <b>350</b> to be discharged through the outlet <b>384</b> to the spray nozzle(s) <b>14</b>. Cooler fluid will then enter through the inlet <b>376</b> and be heated as it flows through the bores <b>440</b> and <b>442</b> and is discharged through the outlet <b>384</b> to the spray nozzle(s) <b>314</b>.

0139Although the controller <b>28</b> can provide separate switchable signals to each of the heater elements <b>372</b> in order to control each heater element <b>372</b> separately under program or logic control, one simple approach includes the bi-metal element or a switch mounted between the power connections to one terminal <b>401</b> and each of the other terminals <b>401</b> connected to the additional heater elements <b>372</b>. The bi-metal element can be set to open at a predetermined temperature, such as 50° C., thereby deactivating the associated heater element <b>372</b>. This enables the additional heater elements <b>372</b>, for example, to remain deactivated until a high heat requirement is initiated.

0140An important feature of the present invention is the ability to easily vary the total surface area of each bore <b>440</b> and <b>442</b> so as to vary the amount of the heat which is supplied to the fluid passing through the bores <b>440</b> and <b>442</b>. A single step offset is shown, by example, in <figref idref="DRAWINGS">FIG. 18</figref>. Alternate the step arrangements are possible.